Transcript CSCE 790: Computer Network Security

CSCE 515:
Computer Network Programming
Chin-Tser Huang
[email protected]
University of South Carolina
Layer 7: Application
Application
Presentation
Session
Transport
Each Layer 7 protocol specifies how one
particular application uses a network.
Each protocol specifies how an application
on one machine makes request and how
the application on another machine
responds.
Network
Data link
Physical
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Layer 6: Presentation
Application
Presentation
Session
Layer 6 protocols specify how to represent
data. They are used to translate from the
representation on one computer to the
representation on another computer.
Transport
Network
Data link
Physical
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Layer 5: Session
Application
Presentation
Session
Transport
Network
Layer 5 protocols specify how to establish a
communication session with a remote
system, including specifications for security
details such as authentication using
passwords.
Data link
Physical
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Layer 4: Transport
Application
Presentation
Session
Transport
Network
Layer 4 protocols specify how to provide
reliable data transfer for different
applications.
Data link
Physical
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Layer 3: Network
Application
Presentation
Session
Transport
Network
Data link
Layer 3 protocols specify how addresses are
assigned and how packets are forwarded
between networks.
Physical
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Layer 2: Data Link
Application
Presentation
Session
Transport
Network
Data link
Physical
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Layer 2 protocols specify how to organize
data into frames and how to transmit
frames over a network.
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Layer 1: Physical
Application
Presentation
Session
Transport
Network
Data link
Physical
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Layer 1 protocols specify details of
interacting with network hardware.
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Origin of Internet
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In the 60’s, US DoD funded ARPANET
for testing new network technologies
ARPANET was later extended to the
Internet
Protocol suite used with Internet is
Transmission Control Protocol/Internet
Protocol (TCP/IP)
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TCP/IP Model in Internet
OSI model
TCP/IP model
Application
Presentation
Application
Session
Transport
Transport
Network
Network
Data link
Link
Physical
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Transport Layer
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Protocol: TCP, UDP
TCP provides a reliable flow of data
between two hosts; including
mechanism of connection setup,
congestion control, and retransmission
UDP provides a simpler service which is
unreliable
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Client-Server Model
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Assume one side of communication is
client, and the other side is server
Server waits for a client request to
arrive
Server processes the client request and
sends the response back to the client
Iterative or concurrent
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Port Number
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TCP and UDP identify applications by
16-bit port numbers
Some servers are assigned well-known
port number
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For example, ftp is port 21 and telnet is
port 23
Clients usually use ephemeral port
numbers between 1024 and 5000
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Network Layer
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Protocol: IP, ICMP, IGMP
Assign addresses to hosts on the
Internet
Determine how to forward messages
over the Internet
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Internet Address
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Every interface on the Internet has a
unique address
In IPv4 every address is 32-bit, while in
IPv6 every address is 128-bit
Usually specified with dotted-decimal
notation: written as 4 decimal numbers,
one for each byte
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hadar.cse.sc.edu: 129.252.130.109
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Classes of Network
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Class A
Class B
Class C
Every network belongs to one of five classes,
based on first byte in its address
0
7
netid
1 0
1 1 0
24
hostid
14
netid
16
hostid
21
netid
8
hostid
Class D
1 1 1 0
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multicast group ID
Class E
1 1 1 1
reserved
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Ranges for Different Classes
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Class
Class
Class
Class
Class
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A: 0.0.0.0 to 127.255.255.255
B: 128.0.0.0 to 191.255.255.255
C: 192.0.0.0 to 223.255.255.255
D: 224.0.0.0 to 239.255.255.255
E: 240.0.0.0 to 255.255.255.255
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Domain Name System (DNS)
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Dotted-decimal addresses are both hard
to remember and meaningless
Use a structured name for each host
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For example, hadar.cse.sc.edu
DNS is a distributed database providing
mapping between IP addresses and
hostnames
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Header Encapsulation
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An application sends messages down
the protocol stack
Each layer adds information to a
message by prepending an extra header
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Header Encapsulation
Application
Transport layer
Network layer
Transport
Network
User data
header
header
Link layer
header
Link
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Application Programming Interface (API)
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A set of operations available to an
application programmer
Two popular APIs
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Sockets developed at Berkeley
X/Open Transport Interface (XTI)
developed by AT&T
We will focus on sockets
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What Is a Socket?
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An API between applications and
network protocol software
provided by the OS
Provide following functions
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Define an abstract endpoint for
communication
Initiate and accept a connection
Send and receive data
Terminate a connection gracefully
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Elements of a Socket
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Each socket can be uniquely identified
by
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Source IP address
Source port number
Destination IP address
Destination port number
An end-to-end protocol (TCP or UDP)
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Types of Sockets
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Two different types of sockets
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Stream sockets
Datagram sockets
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Stream Sockets
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Also known as connection-oriented
socket
Use TCP
Provide reliable, connected
networking service
Error free; no out-of-order packets
Applications: telnet, ssh, http
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Datagram Sockets
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Also known as connectionless socket
Use UDP
Provide unreliable, best-effort
networking service
Packets may be lost; may arrive out of
order
Applications: streaming audio/video
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Next Class
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Socket programming in Java
Read JNP Ch. 14, 16
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